I like the skirmish option. Makes being a pirate more lucrative. And it makes being a trader more frustrating (just a bit mind you) because it is win-win for the pirates. And since you've instituted a new game mechanism, perhaps a new voodoo is called for.
In the game, it has always bothered me that the pirates can never be captured and brought to justice. Of course, their crew would rescue them with some elaborate plan involving bat guano and a parrot. But that would distract from their skirmishing activities. So I propose a new voodoo that would make it so that a player could not skirmish for, say, 72 hours. Call it "The Hanging Tree." It would be a way for the lawfully-minded players to hit back at the pirates, interrupting their skirmish cash flow without affecting fame or fortune unduly.